Generally, passenger seats are provided in a passenger compartment of a vehicle. A driver's seat or passengers' seats include various passenger detecting devices capable of identifying a type of a passenger when the passenger is seated, determining a presence or an absence of the passenger, and indicating whether the seat belt is worn.
Among them, a pattern recognition system, a pressure recognition system, and a weight recognition system are most widely used. In the pattern recognition system, a sensor mat is provided in a seat of the vehicle, and pressure sensors are arranged in a matrix form on the sensor mat, and the passenger is detected and identified by recognizing the weight and pelvic pattern of the passenger seated in the seat.
In the pressure recognition system, a thin bladder and pressure sensors are arranged on a lower side of a seat cushion. When the passenger is seated, the pressure sensors sense the liquid flowing out of the bladder and thus the passenger is detected and identified.
In the weight recognition system, a strain gauge sensor is arranged at a position where a seat frame inside a seat is mounted. Then the weight of the passenger is detected and thus the passenger is detected and identified.
However, even if a variety of the passenger detecting devices are provided as described above, various detection errors occur. For example, if the passenger is seated on one side of the seat or not seated properly, the passenger detecting devices determine that no passenger is seated, or if an underweight adult is seated, the devices identify the passenger as a child.
If the adult passenger is mistakenly identified as a child due to such an error, then when a car accident occurs, an airbag is deployed so as to correspond to the shape of the child which is not safe for an adult, resulting in a secondary injury.
Further, if the passenger is detected as not seated, many problems arise due to an error in identification of the passenger, for example, the passenger may suffer a serious injury because the airbag is not deployed.
In addition to this, since a sensor is required for every seat of the vehicle, not only the cost is increased, but also the information to be processed is increased, and therefore the processing speed is reduced.
Therefore, recently, techniques for detecting the passenger of the vehicle or detecting the number of passengers using images photographed by a camera have been developed.
That is, by referring to FIG. 1, cameras are installed outside a vehicle, that is, on a road and structures near the road, and then images obtained from the cameras are analyzed to measure the number of passengers on the vehicle. Through this, a front seat of the vehicle is confirmed by a camera on the structures, and a rear seat of the vehicle is confirmed by a camera on the roadside.
However, when the camera on the roadside and the camera on the structures are used, it is difficult to confirm the number of passengers on the vehicle when the interior of the vehicle is invisible due to darkness, snow, rain, tinted windshields, etc.